CODEWITHSUNDEEP
pythonpandasdataframe
Dance Party2
Dance Party2

Reputation: 7536

Delete some rows of a column if a value does not exist

Given the following DataFrame:

import pandas as pd
d = pd.DataFrame({'Group':['a','a','c','c'],'Value':[1,1,2,2]})
print(d)

    Group   Value
0   a       1
1   a       1
2   c       2
3   c       2

Since there is no row with a group of 'b', I want to delete any row with a group of 'a'. I only want to delete the 'a' group because there are no rows in the 'b' group.

I know how to get the number of rows in group 'b' like this:

len(d.loc[d['Group']=='b'])

and then do this:

if len(d.loc[d['Group']=='b'])==0:
    d=d.loc[d['Group']!='a']
print(d)

    Group   Value
2   c       2
3   c       2

...but I'm wondering how to work it into the .loc method in one line.

Thanks in advance!

Upvotes: 0

Views: 176

Answers (1)

cs95
cs95

Reputation: 402553

A more intuitive solution to len would be creating a mask and then using .all. After that, just reassign to the filtered slice. 

if ~(d.Group == 'b').all():
     d = d[d.Group != 'a']

d

  Group  Value
2     c      2
3     c      2

You can also use a host of other query methods like df.query and df.*loc.

Upvotes: 1

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